Machine-to-machine (M2M) communication is becoming an increasingly critical consideration in the development of future communication technologies. In M2M communications, machine type communication (MTC) devices such as smart meters, signboards, cameras, remote sensors, laptops, and appliances typically utilize a wireless communication network to transmit data to a receiving host (e.g., a data collection server). MTC devices may differ dramatically from other wireless communication devices (WCDs). For instance, many MTC devices are designed to wirelessly transmit sporadic bursts of one or a few short packets containing measurements, reports, and triggers, such as temperature, humidity, or wind speed readings. In some cases, MTC devices are expected to be installed in a fixed location or have low mobility.
Some M2M services (and devices) often place different requirements on a wireless network than traditional services, such as voice and web streaming. Another distinguishing characteristic in wireless networks with M2M communications is the increasingly large number of MTC devices. Both of these characteristics bring forth new challenges for wireless communication networks to develop a cost, spectrum, and energy efficient radio access technology that can be used in M2M applications and MTC devices.
For example, MTC devices are typically low complexity devices, targeting low-end (low average revenue per user, low data rate, high latency tolerances, etc.) applications. These devices often have severe limitations on power/energy consumption as well as cost. Cost may be understood, for example, with respect to both the cost of manufacturing a device as well as the cost for operating the device. For example, a given device manufactured with a slower processor in the reception chain can have lower manufacturing costs than a similar device with a faster processor. In some aspects, operating costs may be associated with the energy consumed during operation. Several factors can affect the cost of manufacturing and operating a given device. These cost drivers may include, for instance, processing speed (mainly at reception), the number of antennas, and operational bandwidth.
In addition to cost constraints, because of an industry evolution towards M2M communications, the number of radio links between stationary devices is expected to increase significantly in the next generation of communication systems. One reason for this anticipated evolution is the likely increase of wireless backhaul links, due to the expected higher density of radio network deployment and due to the introduction of multi-hop communications involving several hops between communicating end users. Presently, this type of wireless link does not typically require very advanced link adaptation due to the lower degree of radio channel variations.
These differences are compounded by the fact that wireless networks supporting M2M communications may be required to serve a significantly larger number of devices than is typical required in conventional wireless networks, as MTC devices are expected to be cheap and widely deployed. As a result, designing for M2M communications in a wireless communication network creates several challenges.
Considering the anticipated high variety of radio links in the next generation of wireless communications systems, proposals have been provided that target this differing nature of wireless links. For example, it has been proposed to modify the radio interface such that every feature of the physical layer processing can be adapted according to the channel type, traffic to be exchanged, and hardware capabilities of the involved end user devices. In this respect, and upon consideration that future wireless access is likely going to be based in an Orthogonal Frequency Division Modulation (OFDM) variant, it has been proposed to modify the physical resource block (PRB) size and the sub-carrier size, according to the channel variations, device type, and traffic type to be exchanged. The reduction of PRB size is likely related to the lower amount of traffic to be exchanged. The change in sub-carrier size is likely related to the expected lower hardware capability and cost, and consequently, the reduction in energy consumption of the given device involved.
A cyclic prefix (CP) can be used in OFDM systems to, inter alia, mitigate inter-symbol interference (ISI). Such interference is often attributable to multipath propagation. In some cases, the last part of the transmitted symbol is transmitted at the beginning of the symbol. Thus, an ambiguity that might be observed at the end of the frame due to the existence of different symbols can be resolved where the first part of the signal is also used. Presently, in 3GPP LTE (Advanced), there are three different cyclic prefix configurations. In the most common configuration, the cyclic prefix length (in seconds) is equal to 5.2 and 4.7 microseconds, within an OFDM symbol length of 66.67 microseconds. This corresponds to an overhead of 7.24% and 6.59% respectively, if overhead is calculated as the ratio of the cyclic prefix length to the sum of the cyclic prefix and symbol length.